Applied nutritional investigationMigration of the bioelectrical impedance vector in healthy elderly subjects☆
Introduction
Bioelectrical impedance analysis (BIA) is useful for evaluation of the nutritional state in the elderly. Like anthropometry, BIA is a simple non-invasive technique and is particularly suitable for the determination of body composition in epidemiologic investigations and in routine clinical use.
The most frequent method of estimation of the body compartments by BIA is the use of regression equations. These equations generally make use of the predictive power of the resistance index (stature2/resistance) because it is proportional to the mass of conductive tissue in the body.1
In the literature, there are numerous BIA equations for the estimation of body composition, but most of them have been developed from samples of young adults of normal weight. Because various studies have demonstrated that the predictive efficacy of the BIA equations are significantly influenced by age,2, 3 several investigators have proposed specific equations for the estimation of body composition in the elderly.4, 5, 6
However, even the use of age-specific equations could lead to substantial estimation errors.7 Indeed, there is great individual variability in the density of mineral mass, hydration, and protein content of fat-free mass (FFM), and this variability is particularly evident in elderly subjects.8, 9 Moreover, the predictive accuracy of the BIA equations is highly dependent on the body composition of the reference population and on the method of validation.
To avoid the multiplication of population-, sex-, and age-specific BIA equations to predict body composition, which would diminish the comparative value of the results, Piccoli et al.10 proposed the direct use of resistance (R) and reactance (Xc) normalized for stature (H). Bioelectrical impedance vector analysis (BIVA) allows the semiquantitative examination of body composition and provides an evaluation of tissue hydration and nutritional state without the need for descriptive models of the electrical properties of the human body.11 In fact, the length and inclination of the Z impedance vector in the plane delimited by the variables R/H and Xc/H varies according to the state of hydration and soft tissue mass.10
Comparison of the Z vector of an individual or group of individuals with the reference standards of the healthy population12, 13, 14 allows one to evaluate the affinity between the bioelectrical characteristics of the individual or group and those of the population.
Moreover, the position of the Z vector in the RXc plane permits a clinical evaluation of an individual. For example, peculiar impedance characteristics have been described for renal pathologies, liver disease, obesity, cachexia, and anorexia.14 BIVA is particularly useful to study the dynamic variations of the vector, e.g., in follow-up examinations of the state of hydration in dialysis patients or weight changes in the obese.
Because of its characteristics, BIVA is a suitable method to study the quantitative and qualitative changes of body composition in the elderly. It allows simple, inexpensive, non-invasive, and reliable monitoring of variations of the nutritional state during aging and of possible pathologic conditions in the elderly population.
The aim of the present study was to determine the changes of bioimpedance parameters in the elderly. We also want to promote the use of BIVA in gerontology because it is very useful in evaluating body composition changes typical of the aging population.
Section snippets
The sample
The study group, which can be considered representative of the healthy elderly Sardinian population, consisted of 201 individuals (97 men and 104 women) aged 60 to 89 y. The mean ages and standard deviations were 72.7 ± 7.7 y for men and 73.4 ± 7.6 y for women. The sample had rather homogeneous genetic and environmental characteristics because it included subjects born and resident in the province of Cagliari (Sardinia, Italy) whose Sardinian origin was verified to the first parental generation.
Comparison with the Italian standards
The bioelectrical data (R/H and Xc/H) of the male and female samples agreed well with the normal reference values of the Italian population.13 The distribution of the Z vectors in the tolerance ellipses appeared rather homogeneous and centered, as shown in FIG. 1, FIG. 2. In the total male sample (60 to 89 y), 55.6% of cases fell within the 50% tolerance area, 85.5% within the 75% area, and 98.9% within the 95% area. In the female sample (60 to 89 y), 61.5% of cases were within the 50%
Discussion and conclusions
The results of this study showed that healthy elderly subjects present significant changes of bioelectrical parameters with age. Migration of the mean impedance vector in the RXc graph was evident in both sexes and accelerated from the 70- to 79-y to the 80- to 89-y groups. The trend shown by the Z vector was due mainly to reduction of the capacitive component and the consequent decrease of the phase angle.
To date, there have been no specific investigations of changes of the Z vector during
Acknowledgements
The authors thank A. Piccoli and G. Pastori (Department of Medical and Surgical Sciences, University of Padova, Italy) for providing the BIVA software.
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2017, Brain and DevelopmentCitation Excerpt :Concerning the relationship between the PhA and age, there was a significant linear decrease in the PhA according to age in both genders. Previous reports also showed a significant decrease in the PhA with age after the PhA peaks at between 20 and 40 years of age in healthy elderly subjects and healthy adults [6,14,15]. Barbosa-Silva et al. indicated that the decrease in the PhA value with increasing age might reflect the cell function and the general health conditions in addition to the body composition [6].
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This research was financially supported by M.I.U.R. 40% and 60% contributions.